The present invention is directed to a novel scuffer paddle wheel for a sheet handling system and has particular application in an electrostatographic printing apparatus.
In the process of electrophotographic printing, a photoconductive surface is charged to a substantially uniform potential. The photoconductive surface is image wise exposed to record an electrostatic latent image corresponding to the informational areas of an original document being reproduced. This records an electrostatic latent image on the photoconductive surface corresponding to the informational areas contained within the original document. Thereafter, a developer material is transported into contact with the electrostatic latent image. Toner particles are attracted from the carrier granules of the developer material onto the latent image. The resultant toner powder image is then transferred from the photoconductive surface to a sheet of support material and permanently affixed thereto.
This process is well known and useful for light lens copying from an original and printing application from electronically generated or stored originals, and in ionography.
In U.S. Pat. No. 5,014,977 a sheet stopping and lateral registration system is described wherein two paddle wheels having rotating flapper drive units are used to urge sheets toward a pair of scuffer wheels in a duplex tray. Sheets entering the duplex tray have already passed through the fuser and are therefore subject to some curl which frequently inhibits proper stacking and registration and often results in paper jams. The two paddle wheels described in U.S. Pat. No. 5,014,977 minimize this problem by flattening the sheets before they contact the scuffer rolls. Such a system is used in the Xerox 5090 duplicator where the paddle wheel is made of a conventional polyester polyurethane filled with carbon black. While capable of performing adequately this material suffers certain deficiencies, particularly with respect to the variation in the mechanical properties with changes in temperature and relative humidity. The mechanical properties such as resiliency, wear, compression set and tensile set are dynamic properties varying with changes in temperature and relative humidity, thereby, providing unstable sheet feeding performance. In addition, the paddle wheel has a tendency, particularly in the warmer more humid environments, to mark the sheets with black streaks resulting in unacceptable copy quality. Accordingly, there is a need for an improved scuffer paddle wheel having a more stable response in mechanical properties, particularly resiliency to variations in temperature and relative humidity, and in particular, having better wear and compression set characteristics as well as not adding black streaks to the copies.